Linear homopolymer chains in poor solvent exist either as individual crumpled single chain globules or asmacroscopic precipitate

depending on whether the solution is in the one- or the two-phase region. However

linearheteropolymer chains in dilute solution might be able to form stable mesoglobules made up of a limited number of chains ifthe degree of amphiphilicity of the chain is sufficiently high and the experimental conditions are appropriate. The self-assembly of block copolymers in a selective solvent is typical of such examples.In practice

the formation of stable mesoglobules can be directly related to the formation of novel polymeric nanoparticles in solution.In this article

we will address the formation of mesoglobular phase not only on the basis of thermodynamics

but also from a kinetic point of view

which leads to the discussion of how viscoelasticity can affect the phase behavior of heteropolymer chains in dilute solution.The formation and stabilization of several different kinds of novel polymeric nanoparticles will be used to illustrate our discussion.